Page 212 - Maths Skills - 8

210 Maths

INTRODUCTION
Sometimes a piece of information is complicated and hence difficult to study and understand. So it needs an
illustration. For example, if we need to study the interest rates on home loans, as charged by a bank from time
to time over a period of 20 years, it will be much easier to study the information visually. Graphs communicate
information visually.
Graph is a handy tool both for systematic presentation and easy understanding of data. This is the reason that
graphs are often used in newspapers and magazines all over the world.

You have studied about graphs in the chapter Data Handling. You already know about
● Bar graphs: used to compare two or more quantities
● Double bar graphs: used to compare two sets of data simultaneously
● Pie chart: used to compare the part and the whole
● Histogram: used to show the data given by a frequency distribution table

In this chapter, we will learn to determine the position of a point in a plane with reference to two mutually
perpendicular straight lines.

COORDINATE GEOMETRY
Suppose, we want to inform about our location to our friend. Can we use the number line as reference? No,
because a location needs use of directions and distance.
To solve this problem, Rene Descartes, a famous Mathematician introduced a two dimensional system, i.e., a plane
called Cartesian System. The branch of mathematics that involves this system is called Coordinate Geometry.

CARTESIAN SYSTEM
A point in a plane can be denoted with reference to the axes system. It has a horizontal line X′OX called x-axis and
a vertical line YOY′ called y-axis. The point of intersection of these two axes is called the origin denoted by ‘O’.
Fig. shows the Cartesian plane.

Parts Quadrant Signs of the
Coordinates
XOY I (+, +)

YOX′ II (–, +)
X′OY′ III (–, –)

Y′OX IV (+, –)

As we have observed, the plane is divided into 4 parts. Each of these parts is termed as Quadrant. These quadrants
are named as first, second, third and fourth quadrants respectively in anticlockwise direction. We can summarize
the above information as given in above table.